Datasheet

EN
95%
5%
V
OUT
t
Start
t
RAMP
TPS65070, TPS65072, TPS65073
TPS650731, TPS650732, TPS650701, TPS650702, TPS650721
SLVS950G –JULY 2009–REVISED MAY 2013 www.ti.com
100% Duty Cycle Low Dropout Operation
The device starts to enter 100% duty cycle Mode once the input voltage comes close the nominal output voltage.
In order to maintain the output voltage, the High Side MOSFET switch is turned on 100% for one or more cycles.
With further decreasing V
IN
the High Side MOSFET switch is turned on completely. In this case the converter
offers a low input-to-output voltage difference. This is particularly useful in battery-powered applications to
achieve longest operation time by taking full advantage of the whole battery voltage range.
The minimum input voltage to maintain regulation depends on the load current and output voltage, and can be
calculated as:
Vin
min
= Vout
max
+ Iout
max
× (RDSon
max
+ R
L
) (3) (3)
With:
Iout
max
= maximum output current plus inductor ripple current
RDSon
max
= maximum P-channel switch RDSon.
R
L
= DC resistance of the inductor
Vout
max
= nominal output voltage plus maximum output voltage tolerance
Under-Voltage Lockout
The under voltage lockout circuit prevents the device from malfunctioning at low input voltages and from
excessive discharge of the battery and disables the DCDC converters and LDOs. The under-voltage lockout
threshold is configurable in the range of typically 2.8V to 3.25V with falling voltage at the SYS pin. The default
undervoltage lockout voltage as well as the hysteresis are defined in register CON_CTRL2. The default
undervoltage lockout voltage is 3.0V with 500mV hysteresis.
SHORT-CIRCUIT PROTECTION
The High Side and Low Side MOSFET switches are short-circuit protected with maximum output current = ILIMF.
Once the High Side MOSFET switch reaches its current limit, it is turned off and the Low Side MOSFET switch is
turned. The High Side MOSFET switch can only turn on again, once the current in the Low Side MOSFET switch
decreases below its current limit.
Soft Start
The 3 step-down converters in TPS6507x have an internal soft start circuit that controls the ramp up of the output
voltage. The output voltage ramps up from 5% to 95% of its nominal value within typ. 250μs. This limits the
inrush current in the converter during start up and prevents possible input voltage drops when a battery or high
impedance power source is used. The Soft start circuit is enabled after the start up time t
Start
has expired.
During soft start, the output voltage ramp up is controlled as shown in Figure 31.
Figure 31. Soft Start
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